The sender node MUST send the following options in the Advertisement
message:
Source Link-Layer Address The link-layer address of the sender.
Target Link-Layer Address
The link-layer address of the target, that is, the sender of
the advertisement.

It should say:

The sender node MUST send the following options in the Advertisement
message:
Source Link-Layer Address
The link-layer address of the node transmitting the
Advertisement message
Target Link-Layer Address
The link-layer address of the node that transmitted the
Solicitation message

Notes:

There is an ambiguity with the Source Link-Layer and Target Link-Layer Address option in the Inverse Neighbor Discovery Advertisement Message. It is unclear if SLLA is set to sender of the Advertisement or of the Solicitation, the same with TLLA. The RFC-text as it is would lead to SLL=TLL=sender of advertisement.

Here is an example for clarification of the problem (with 2 Ethernet-nodes, no FR):
Eth Node A - Eth Node B:
1. A sends IND S with SLLA=A, TLLA=B
2. B takes the address pair from SLLA and source-IP in ND cache
3. B answers with IND A with TAL(identified by TLLA in solicitation), SLLA=B,TLLA=B <- problem is here (SLLA=TLLA=B). Is that acceptable?
Or modify to: SLLA=A or TLLA=A? Or omit TLLA?
4. A takes the address pair from SLLA and the TAL in ND cache

Solution 1: B answers with IND A with TAL, SLLA=B, and TLLA=A => Then carries TLLA the address of the requesting node (is that acceptable as “target” address?)

Solution 2: B answers with IND A with TAL, SLLA=A, and TLLA=B => Then A could not take the address pair from SLLA and the TAL in ND cache.